Cover Crops Impact Soil Health

Planting cover crops is becoming a common practice, however; producers may not be sure what is the impact of cover crops on soil health. Andy Clark (USDA-SARE, 2015) outlines key ways that cover crops lead to better soil health and potentially better farm profits.

Cover crops feed many types of soil organisms including soil fungi and bacteria that are beneficial to crops. Microbes feed on carbohydrates that plants roots exude (release) and in return; trade nutrients such as nitrogen, phosphorus, and micronutrients to crop roots. Many other soil organisms eat the fungi and bacteria, recycling those nutrients back to the plant.

Cover crops increase the number and types of earthworms in the soil. Nightcrawlers tunnel vertically, while redworms tunnel horizontally. Both earthworms create channels for crop roots to grow and for rainfall and air to move into the soil while inoculating the soil with microbes. Cover crops and live roots help support the entire soil food web throughout the year. Cover crops build soil carbon and soil organic matter (SOM) by using sunlight and carbon dioxide to build soil carbon. High levels of SOM improve plant available nutrients, increases soil moisture for crops, and improves crop growth. Every 1% increase in SOM increase crop yields 12%. With better management of soil nutrients, cover crops gradually change fertilizer needs. Cover crops scavenge and tie up left over fertilizer nutrients at the end of a growing season, like nitrogen and phosphorus, which improves water quality. By improving fertilizer use efficiency over time, crop yields and farmers profits increase while the environment is safer due to less nutrient runoff.

Cover crops help keep the soil covered. When it rains on bare soil, the soil is much more likely to erode, form an impermeable crust and then overheat in summer when exposed to direct sun. Some bare soils can reach 140 degrees, hot enough to kill soil organisms and stress the crop from both heat and excessive soil moisture evaporation. Cover crop residue like cereal rye protects soil by keeping it cooler while the cash crop is getting established. In most of the USA, almost half the topsoil has been lost to erosion. Cover crops are exceptional at stopping erosion. Using no-till with cover crops reduces soil erosion to 1/10 to 1/100 the normal erosion rate of conventional tilled crops. Even with light tillage, winter annual cover crops protect soil. The extra rain and water that infiltrates soil instead of running off increase crop yields. In mid-to-late summer in the Midwest, rain can come fast in thunderstorms and be followed by long dry spells. The extra aeration created by cover crop roots and earthworms benefits most soil organisms and the following grain crop.

Cover crops improve plant and microbial diversity. The longer living roots are growing, the more biodiversity there will be in soil organisms, leading to healthier soil. Growing mixes of cover crops in a rotation—such as cereal rye before soybeans, and oats, radishes or Balansa clover before corn—improves diversity. With more wheat planted this year, a diverse cover crop mix can be planted for several months. For livestock producers, these crops can be grazed, harvested for forage, or used to apply and recycle manure nutrients. Some cover crop species can be grown for high-quality forages in late fall or early spring, improving farmer profits. Cover crops reduce soil compaction and improve soil structure. Most conventional farmers try to use tillage to solve soil compaction, but that is a brief solution and actually makes soil compaction worse. Tillage destroys soil structure by aerating the soil, causing roots exudates and glues to be lost. Cover crops and soil organisms create the glue (glomalin) that binds soil particles together, leading to better soil aggregation and strong soil structure. Research shows that cover crops loosen compacted soil more effectively than subsoiling, which takes a lot of diesel fuel. A field with cover crops and minimal tillage, or better yet no-till, leads to much better soil structure without compaction issues; however, it may take 1-3 years longer to achieve.

Soil health is a hot topic these days, one that is receiving considerable attention from farmers. In the past, soil testing focused mostly on chemical and physical measurement, but now new research has shown that soil biology is important to soil health and crop productivity. Cover crops feed the soil organisms and vice versa. From learning more about soil biology, even a modest use of cover crops makes a big difference in soil health!